1. Field of the Invention
The present invention relates to vapor recovery apparatus and, in particular, to using recovered vapor for power generation.
2. Description of Related Art
Since the passage of the Clean Air Act, the Congress of the United States has required all persons or organizations handling hydrocarbons or chemicals whose vapors may pollute the air to install means to recover and prevent the contamination of the air by such vapors. Such contaminants can include vapors of gasoline, methylene chloride and other organic compounds.
Such vapors are generated and displaced into the atmosphere when all types of tanks are filled with liquid hydrocarbons or liquid chemicals. Such tanks may be large storage tanks, railroad car tanks, truck tanks, underground storage tanks for gasoline stations and fuel tanks on trucks, buses and automobiles. When these various types of tanks are filled with liquid hydrocarbons or liquid chemicals, vapors escape into the atmosphere and, as is well known, such vapors become a source of smog, which under certain ambient conditions produce dangerous fog conditions and so pollute the atmosphere that they produce dangerous environmental health hazards for human beings.
Known vapor recovery systems have used closed refrigeration cycles to cool a medium that is then used to condense vapors. Condensate can be drained to a decanter to separate heavy and light constituents, such as gasoline and water. The condensing coils for such units are periodically warmed or defrosted to prevent a build up of ice and frost that may block the passage of vapors through the condensing unit. See for example, U.S. Pat. Nos. 4,027,495; 4,068,710; 4,077,789; and 5,291,738.
Such recovery units are typically designed to handle the peak flow of vapors that may be experienced during a course of a work day. To accommodate the peak load, the recovery units are engineered with a relatively high capacity, which still may not be sufficient condense highly volatile vapors.
A disadvantage with vapor recovery systems is the energy required to run these recovery systems. Moreover, certain highly volatile vapors can only be condensed after a high expenditure of energy. Accordingly, the environmental benefits of performing vapor recovery is partially offset by the additional energy consumed to run the recovery systems.
Many industries are economically dependent on inexpensive and abundant electrical power. Many utilities will charge a rate that depends upon the peak usage or the time when the peak usage occurs. For this reason, some industries have invested in cogeneration, wherein a modest private plant for generating electricity will supplement the power from a utility to reduce the peak demand and thereby reduce the rate charged for power. Depending upon the size of the plant, some cogeneration systems can actually return power to the utility lines to earn a credit.
While in principal, a cogeneration plant can be powered by the uncondensed vapor from a vapor recovery unit, the supply of vapor tends to be sporadic and will lack a constancy that will allow cogeneration to occur in a practical way.
Such a cogeneration system may employ a generator driven by an engine that is designed to be powered by a fossil fuel. When the engine is an internal combustion engine, regulating the air/fuel ratio can be difficult when the fuel source is the uncondensed vapor from a vapor recovery unit. The uncondensed vapor can include a variety of vapors whose constituent components cannot be known in advance. Therefore, regulating the speed and power of the engine can be difficult, when the nature of the fuel, and the fuel to air ratio may vary significantly.
Furthermore, one cannot be certain in advance that the combination of a vapor recovery unit and cogeneration system will succeed in providing a net environmental benefit. In particular, the engine exhaust may introduce significant pollutants that should not be exhausted to the atmosphere.
Accordingly, there is a need to recover vapors using a combination of effective techniques such as condensing vapors, as well as using those vapors that were not condensed, in a power generation system.